The investigator has two specific aims. The first is to study genetic diversity and phylogeny among naturally-occurring SIVs from African non-human primates. The author will attempt to more rigorously define viral evolution and divergence of SIVagm (SIV in African Green Monkeys) viruses in relation to their host species. Full-length clones of SIVagm(sab) from West African green monkeys and SIVagm(tan) from tantalus monkeys will be sequenced and compared with two other species of African green monkeys (vervet and grivets). Additional SIVagm (gri) and SIVabm(ver) viruses will be analyzed to determine whether species-specific SIVagm viruses from vervet, grivet, sabaeus and tantalus monkeys have evolved and diverged coincident with their respective host species. In addition, the author will expand genetic studies to include viruses from other monkey species within the Cercopithecus genus, including Patas and Hamlyn's monkeys. The second goal of the investigator is to define and compare viral and host determinants of pathogenesis for naturally-occurring SIVs. The purpose of this aim is to define viral and host factors which play a role in determining natural resistance to disease. Certain strains of SIVagm may be more pathogenic than others. The study of more pathogenic strains of SIVagm strains may lead to the identification of specific determinants directly involved in pathogenesis. Both molecular and biologic clones derived from green monkeys with SIV-related abnormalities will be further studied in the green monkey animal model.